This invention relates to production of false-twist textured yarn of polyester filaments, and is more particularly concerned with yarns of polyester filaments having a random distribution of thick and thin sections which differ in dye uptake.
Conventional processes for producing textile yarns of polyester filaments have involved melt-spinning polyethylene terephthalate into yarn at take-off speeds of 550 to 1640 yards per minute (500 to 1500 meters/minute). The take-off speed refers to the speed of the solidified yarn at windup or a roll for forwarding the yarn to subsequent processing. This as-spun yarn is usually drawn at a draw ratio of about 3.5 to 4.5.times. (3.5 to 4.5 times greater length) to produce the fully-drawn, uniform yarn of commerce.
Conventional as-spun yarn can be drawn to provide a random distribution of thick and thin sections along the filaments, of which the thick sections have a higher dye uptake (dye to darker shades) and provide attractive dyed fabrics.
Werner et al. U.S. Pat. No. 3,478,143 discloses such a process in which conventional as-spun yarn is incompletely drawn on a draw pin of about 1.5 to 6 cm in diameter maintained at a temperature of 60.degree. to 105.degree. C. (preferably 65.degree. to 85.degree. C.), using a draw ratio of about 60 to 80 percent, preferably 66 to 74 percent, of the draw ratio normally used for producing uniform fully drawn yarn. However, yarns produced in this way have not been suitable for producing textured (crimped) yarn by modern false-twist texturing processes because the thick sections stick or melt on contacting the texturing heater used to set twist in the yarn. Heater temperatures above 200.degree. C. are needed to obtain satisfactory crimp properties.
Petrille U.S. Pat. No. 3,771,307 discloses that polyester yarn can be false-twist textured under conventional conditions, at heater plate temperatures of 227.degree. C. to produce excellent textured products when using spin-oriented yarn prepared by melt-spinning at take-off speeds of 3000 to 4000 yarns per minute (2744 to 3660 meters/minute). The as-spun yarn is drawn at a draw ratio of 1.3 to 2.0 which is sufficient to provide a fully drawn, uniform yarn. The patent does not refer to production of thick and thin sections along the filaments. Schippers German OS Patent No. 2,204,397 (laid open Aug. 9, 1973) discloses melt-spinning polyester yarn at take-off speeds higher than 3000 meters/minute (3280 yards/minute) to form a spin-oriented yarn which is then drawn at a draw ratio in the range of 1.3 to 1.8.times. to produce a fully drawn product. The process is said to avoid denier variations caused by local instability of the draw point when yarn is spun at conventional take-off speeds of 500 to 1500 meters per minute (550-1640 yards/minute). The patent teaches that no well defined and therefore locally determined draw point forms when drawing the spin-oriented yarn, and that hot pins are not required.